The importance of oncogenes in the development of human cancer has been amply demonstrated in recent years by the ability of these genes to cause tumorigenic conversion of rodent cells. There can be no doubt that other human genes exist which are not classified as oncogenes per se but which play important roles in the development and progression of cancer. One category of these genes encodes abundant structural proteins such as the actins and tropomyosins. The involvement of these abundant proteins in the neoplastic transformation process is suggested by the well documented observations that isoforms within these structural protein families are consistently modulated in transformation of avian, rodent and human cells. This second category of cancer-related genes is set apart from the so-called "oncogenes" because modulation of these genes in a transformation-sensitive manner is likely to result from regulatory processes activating transcription or translation rather than by direct activation through mutational processes.
An abundant phosphorylated polypeptide, plastin is frequently expressed in human cancer cells of solid tissue but is not expressed in normal human fibroblasts. The same protein was one of the most abundant constitutively expressed proteins of human white blood cells. Thus, plastin may be associated with transformation of non-hemopoietic cells. Despite the reproducible identification of plastin and studies of its expression and polymorphic character, nothing was known of its molecular identity.